Rigid polyurethane foams

ABSTRACT

Polyurethane foams containing a syntactic phase and a cellular, non-syntactic phase are useful as reinforcing foams, such as in automotive applications. The foams are conveniently made in the reaction of a high viscosity isocyanate-reactive component and a high-viscosity polyisocyanate component, at least one of which contains a plurality of hollow microspheres.

BACKGROUND OF THE INVENTION

The present invention relates to rigid polyurethane foams. Morespecifically, the present invention relates to novel rigid syntacticpolyurethane foams that are particularly useful as reinforcementmaterials, especially in the auto industry.

Rigid foams have been used in the auto and other industries for a numberof purposes. For example, rigid foams have been used in the auto andother industries for structural reinforcement, preventing corrosion anddamping sound and vibration.

Generally, to be useful as reinforcing foams in automotive applications,it is desirable for rigid foams to have a good balance between densityand physical properties such as compression strength. One way that hasbeen tried to accomplish this is to use so-called syntactic foam.Syntactic foams are composites consisting of hollow microspheres (minutehollow bubbles, microbubbles, or microballoons) that are dispersed in aresinous matrix. These microspheres are commonly made from inorganicmaterials such as glass and silica; and polymeric materials such asepoxy resin, unsaturated polyester resin, silicone resin, phenolics,polyvinyl alcohol, polyvinyl chloride, polypropylene, and polystyrene.One example of syntactic foam known in the art to be used as structuralfoam is sold by Novamax industries under the tradename “Novacore”. Thisproduct uses an epoxy as the continuous resinous matrix.

In these syntactic foams, the resinous matrix is typically substantiallynon-cellular. However, because the microspheres are hollow, theirinclusion reduces the density of the syntactic foam. Thus, essentiallyall of the reduction in density (relative to that of the unfoamed epoxymatrix) is attributable to the gas contained in the microspheres. Insome instances the epoxy matrix is expanded slightly by incorporatinginto it expandable plastic spheres and/or thermally decomposable blowingagents such as azodicarbonamide or p,p-oxybis(benzene sulphonylhydrazide). However, the limit of expansion of these materials isusually 80% or less, and applied heat is required in order to obtaineven this small amount of expansion.

Although one and two part epoxy-based syntactic foams have enjoyed somesuccess as reinforcing foam in the auto industry, they suffer from somedeficiencies. First, epoxy-based syntactic foams are cured by applyingheat. In automotive applications, it is frequently difficult to supplysufficient heat to get the epoxy-based syntactic foams to curethroughout the part. Consequently, portions of the foam may be curedwhile other portions, especially the center of the foam, may be leftuncured. Moreover, curing is often done in E-coat and paint cure ovens,which often do not maintain close control over curing temperatures. Thiscan lead to incomplete fills or undercuring when oven temperatures aretoo low. Undercuring can lead to the foam having a low T_(g), so that itbecomes soft and loses its reinforcing effect when warm, such as undersummertime conditions. Conversely, oven temperatures that are too highoften lead to chemical reaction exotherms resulting in foam scorching,charring, overexpansion or even paint blistering if the exotherm is toohigh.

Second, epoxy-based syntactic foams are generally very brittle and thuslack fracture toughness. Therefore, these foams tend to shatter onimpact (such as in a vehicle collision) or crack easily under stress.

Third, it is difficult to make a suitable epoxy-based syntactic foam ata density lower than about 27-35 pcf. At lower densities, those foamsbecome extremely brittle. However, having a lower density is veryimportant to automobile manufacturers, particularly when the vehiclecontains a large amount of the reinforcing foam. The lower densitytranslates into lower foam weight, thereby decreasing the overall weightof the vehicle. Reduced weight often correlates to lower fuelconsumption and therefore, lower vehicle operating cost.

Rigid, non-syntactic polyurethane foams have also been used asreinforcing foams in automotive applications. These polyurethane foamsare formed by the reaction of a polyisocyanate compound such as toluenediisocyanate (TDI) or diphenylmethane diisocyanate (MDI) or polymericMDI with an isocyanate-reactive component, such as a polyol or water.Generally, streams of the isocyanate-reactive component andpolyisocyanate are intermixed in a mixing head (together with a blowingagent, if water is not included in the formulation) and then dispensedinto a cavity or mold. In the mold or cavity, the isocyanate-reactivecomponent and the polyisocyanate react to form the polyurethane. Anywater present in the formulation will react with the polyisocyanate toform carbon dioxide gas. The carbon dioxide gas causes the foaming massto expand, resulting in a non-syntactic cellular structure.

These non-syntactic polyurethane foams have the advantage that they canbe formed at very low densities, thereby decreasing the overall weightof the foam. However, the raw materials used to make these foams aretypically liquids having a low viscosity, typically about 1000 cps orless. This causes a problem in automotive applications, because thereaction mixture is usually applied to structural members of the vehiclethat are not primarily designed as molds for the foam. These structuralmembers include vertical surfaces or cavities that are not completelysealed. For example, these members may contain openings such as trimattachment holes, unsealed seams, drain flutes and the like.Consequently, the low-viscosity reaction mixture readily leaks throughany small openings in the cavity, or flows away from non-horizontalsurfaces. In addition, it is often desired to reinforce only certainportions of a particular part. In order to accomplish this with thesepolyurethane foam formulations, it is necessary to install baffles ordams inside of the part or cavity to insure that the mixture is confinedin the desired area. This adds considerable cost to the process.

One approach to overcoming these problems with polyurethane foams is tofroth the reaction mixture. Frothing is typically done by mechanicallywhipping air or other gas into the polyurethane mixture using a highshear mixer. When a frothing method is utilized, leakage is reducedbecause the reaction mixture leaving the mix head has a creamy, moreflow resistant consistency. However, a large enough quantity of gas mustbe whipped into the reaction mixture to create a flow resistantconsistency, and this can ultimately result in a foam having too low adensity to provide adequate reinforcement.

Another approach to solving these problems of polyurethane foams is toselect highly reactive components so that the reaction mixture hasextremely short gel time. However, these formulations tend to be highlyexothermic, so precautions must be taken to prevent the heat generatedduring the reaction from producing temperatures high enough to causefoam scorching or even a foam fire. In addition, these highly reactivemixtures tend to split when used to make larger volume foams. Therefore,these highly reactive mixtures are often used to successively apply thinlayers of polyurethane foam or in smaller amounts than are needed tofill the cavity. This greatly limits the range of applications for whichthese highly reactive mixtures are useful.

SUMMARY OF THE INVENTION

In one aspect, this invention is a polyurethane foam having a bulkdensity from about 7 to 35 pounds per cubic foot and a compressivemodulus of at least 5,000 psi as measured by ASTM D 1621 for a 2″×2″×1″skinless core foam sample at a deflection rate of 0.1 inch/minute, saidfoam comprising a non-syntactic cellular polyurethane matrix havingdispersed therein from about 5 to about 35 weight percent, based on theweight of the foam, of a syntactic phase comprising hollow microspheres.The foam of this aspect of the invention provides a unique combinationof moderately low density and good physical characteristics,particularly compressive modulus. The foam is especially suitable foruse as a reinforcing foam, especially for automotive applications, as itis easily foamed in place where reinforcement is needed and is easilyformulated so that it does not require applied heat to cure.

In a second aspect this invention is a polyurethane foam made by (1)mixing under reaction conditions a high viscosity isocyanate-reactivecomponent (a) and a high viscosity polyisocyanate component (b), whereincomponent (a) includes at least one polyol, a blowing agent and at leastone thixotropic agent, and component (b) includes at least onepolyisocyanate compound and at least one thixotropic agent, wherein oneor both of components (a) and (b) contain a plurality of hollowmicrospheres, and (2) allowing the mixture to expand in place and cure.

Because the foam of the invention contains both microspheres and acellular polyurethane matrix, the foam is easily made with a combinationof desirable density and good physical properties, particularlycompression modulus. As it is easily made from high viscositycomponents, it is easily applied to a variety of structures that requirereinforcement. When applied, the high viscosity reaction mixture staysin place until it expands and cures to form the desired reinforcingfoam. The reaction mixture generally cures without application of heat,thereby eliminating a costly heating step.

DETAILED DESCRIPTION OF THE INVENTION

The foam of the present invention includes both a continuous,non-syntactic, polyurethane foam phase and a syntactic phase. Thecontinuous, non-syntactic, polyurethane foam phase is created by thechemical reaction of the aforementioned polyol and polyisocyanatecomponents, together with the formation of gas from the blowing agent.The syntactic phase comprises hollow microspheres that are dispersed inthe polyurethane foam matrix. The foam has a bulk density of from about7 pounds per cubic foot (pcf), preferably from about 10 pcf, morepreferably from about 15 pcf, to about 35 pcf, preferably to about 30pcf, more preferably to about 25 pcf. The foam has a compressive modulusof at least 5000 psi, preferably at least 10,000 psi, more preferably atleast 15,000 psi, to about 30,000 psi, more preferably to about 25,000psi, as measured on a 2″×2″×1″ skinless core sample of the foam at adeflection rate of 0.1 in/minute. The microsphere content of the foam isadvantageously from about 5, preferably about 10, more preferably about12 weight percent, to about 35, preferably about 30, more preferablyabout 20 percent of the total weight of the foam.

The reactive components of the foam are preferably expanded at leastabout 100%, more preferably at least 150%. The amount of expansion isdetermined in the following manner:

(a) the volume of the reactive components in the foam mixture isdetermined;

(b) the volume of the non-reactive components in the foam mixture isdetermined;

(c) the volume of the final foam is determined;

(d) the volume of the polyurethane matrix of the final foam isdetermined by subtracting the volume of the non-reactive components fromthe volume of the final foam, respectively; and

(e) calculating the % expansion using the formula

% Expansion=[(V _(e) /V _(i))-1]×100%,

where V_(e) is the volume of the polyurethane matrix of the final foamand V_(i) is the volume of the reactive components in the foam mixture.The reactive components include polyols, water, crosslinkers,amine-initiated polyols, amine-functional materials and polyisocyanates,all as described more fully below. Non-reactive components include allother materials that do not react into the polymer network, includingmicrospheres, catalysts, thixotropic agents, surfactants, fillers,non-reactive plasticizers and the like.

The foam of the invention is conveniently made by reacting a highviscosity isocyanate-reactive component with a high viscositypolyisocyanate component. Each component is sufficiently high inviscosity (at low or zero shear) that when the components are mixed, theuncured reaction mixture exhibits minimal or preferably no flow underthe force of gravity and in the absence of shear at applicationtemperatures of about 60-100° F. Preferably, the viscosity andcompatibility of each component is also such that there is substantiallyno separation of liquid and solid (filler) ingredients over a prescribedperiod, such as three months or longer at 50-100° F.

These requirements are generally met when the isocyanate-reactivecomponent has a Brookfield viscosity (#7 spindle, 25° C., 10 rpm) offrom about 50,000 cps, preferably from about 100,000 cps, morepreferably from about 125,000 cps, most preferably from about 150,000cps to about 400,000 cps, preferably to about 300,000 cps, morepreferably to about 250,000 cps. The polyisocyanate component suitablyhas a Brookfield viscosity (same conditions) of from about 50,000 cps,preferably about 100,000 cps, more preferably 150,000 cps mostpreferably about 200,000 cps to about 400,000 cps, preferably to about300,000 cps, more preferably to about 250,000 cps.

The polyol component and the polyisocyanate component preferably havesimilar viscosities. If the components have significantly differentviscosities, then effective mixing and dispensing becomes moredifficult. Generally, the difference between the viscosity of the polyolcomponent and the viscosity of the polyisocyanate component is nogreater than about 150,000 cps, more preferably no greater than about100,000 cps and most preferably no greater than about 50,000 cps.

The high viscosity isocyanate-reactive component includes at least onepolyol, a blowing agent and a thixotropic agent. It will usually containa surfactant, and may contain other additives as described below.

The polyol is one or more compounds having at least twoisocyanate-reactive hydroxyl groups per molecule. As is discussed morefully below, mixtures of two or more polyols together with otherisocyanate-reactive compounds are preferred. In general, suitablepolyols include compounds nominally having from about 2 to about 8isocyanate-reactive hydroxyl groups per molecule. The hydroxylequivalent weight of the individual polyols may range from about 31 toabout 2000 or more. Suitable polyols include compounds such as alkyleneglycols (e.g., ethylene glycol, propylene glycol, 1,4-butane diol, 1,6hexanediol and the like), glycol ethers and polyethers (such asdiethylene glycol, triethylene glycol, dipropylene glycol, tripropyleneglycol and the like), glycerine, trimethylolpropane, tertiaryamine-containing polyols such as triethanolamine, triisopropanolamine,and ethylene oxide and/or propylene oxide adducts of ethylene diamine,toluene diamine and the like, polyether polyols, polyester polyols, andthe like. Among the suitable polyether polyols are polymers of alkyleneoxides such as ethylene oxide, propylene oxide and 1,2-butylene oxide ormixtures of such alkylene oxides. Such polyether polyols have a hydroxylequivalent weight of from about 200 to about 2000 or more. Preferredpolyethers are polypropylene oxides or polymers of a mixture ofpropylene oxide and a small amount (up to about 12 weight percent)ethylene oxide. These preferred polyethers may be capped with up toabout 30% by weight ethylene oxide.

Polyester polyols are also suitable. These polyester polyols includereaction products of polyols, preferably diols, with polycarboxylicacids or their anhydrides, preferably dicarboxylic acids or dicarboxylicacid anhydrides. The polycarboxylic acids or anhydrides may bealiphatic, cycloaliphatic, aromatic and/or heterocyclic and may besubstituted, such as with halogen atoms. The polycarboxylic acids may beunsaturated. Examples of these polycarboxylic acids include succinicacid, adipic acid, terephthalic acid, isophthalic acid, trimelliticanhydride, phthalic anhydride, maleic acid, maleic acid anhydride andfumaric acid. The polyols preferably have an equivalent weight of about150 or less, and include ethylene glycol, 1,2- and 1,3-propylene glycol,1,4- and 2,3-butane diol, 1,6-hexane diol, 1,8-octane diol, neopentylglycol, cyclohexane dimethanol, 2-methyl-1,3-propane diol, glycerine,trimethylol propane, 1,2,6-hexane triol, 1,2,4-butane triol,trimethylolethane, pentaerythritol, quinitol, mannitol, sorbitol, methylglycoside, diethylene glycol, triethylene glycol, tetraethylene glycol,dipropylene glycol, dibutylene glycol and the like. Polycaprolactonepolyols such as those sold by Union Carbide Corporation under the tradename “Tone” are also useful.

Aromatic polyester polyols are a preferred type of polyol to use as aprimary polyol ingredient of the isocyanate-reactive component, becausethey provide good rigidity to the foam at a given molecular weight. Thepreferred aromatic polyester polyols include esters of orthophthalicacid or orthophthalic anhydride and a glycol or glycol ether such asethylene glycol or diethylene glycol. The preferred aromatic polyesterpolyols have a nominal functionality of about 2.0 and an equivalentweight from about 125-225, more preferably about 150-200. These aromaticpolyester polyols are characterized in having a relatively highBrookfield viscosity, such as from about 2000 to 3000 cps @ 25° C.

It is also preferred to employ, in conjunction with the preferredaromatic polyester polyol, one or more very low (up to about 125)equivalent weight tri- or higher-functional polyols. These polyols areoften referred to as “crosslinkers”. Among these are glycerine,trimethylolpropane, and the like. These crosslinkers generally comprisea minor amount by weight of the isocyanate-reactive component, such asfrom about 2 to about 40 weight percent, based on the weight of thearomatic polyester polyol.

In order to impart toughness to the foam, a minor amount of a high (i.e.800 or higher, preferably about 1500-3000) equivalent weight polyol maybe added to the isocyanate-reactive component, as well. This highequivalent weight polyol is preferably a polyether polyol having two tothree hydroxyl groups per molecule. It more preferably is apoly(propylene oxide) that may be end-capped with up to 30% (by weightof the compound) of poly(ethylene oxide). A particularly preferred highequivalent weight polyol contains dispersed polymer particles. Thesematerials are commercially known and are commonly referred to as“polymer polyols” (or, sometimes “copolymer polyols”). The dispersedpolymer particles may be, for example, polymers of a vinyl monomer (suchas styrene, acrylonitrile or styrene-acrylonitrile particles), polyureaparticles or polyurethane particles. Polymer or copolymer polyolscontaining from about 2 to about 50% or more by weight dispersed polymerparticles are suitable. When used, this polymer or copolymer polyol mayconstitute up to about 45%, preferably from about 5 to about 40%, of theweight of all isocyanate-reactive materials in the isocyanate-reactivecomponent.

It is preferred to incorporate at least a small amount of a tertiaryamine-containing polyol in the isocyanate-reactive component. Thepresence of this tertiary amine-containing polyol tends to increase thereactivity of the isocyanate-reactive component during the early stagesof its reaction with the polyisocyanate. This in turn helps the reactionmixture to build viscosity more quickly when first mixed and applied,without unduly decreasing cream time, and thus reduces run-off orleakage. Such tertiary amine-containing polyols include, for example,triisopropanol amine, triethanolamine and ethylene and/or propyleneoxide adducts of ethylene diamine having a molecular weight of up toabout 400. The tertiary amine-containing polyol advantageouslyconstitutes up to about 10, preferably up to about 5 percent of thecombined weight of all isocyanate-reactive materials in theisocyanate-reactive component.

The isocyanate-reactive component may further comprise a small quantityof an amine-functional compound having one or more terminalisocyanate-reactive amine groups. These include polyols having a primaryor secondary amine group, such as monoethanolamine, diethanolamine,monoisopropanolamine, diisopropanol amine and the like, and aliphaticamines such as aminoethylpiperazine. Also included among these compoundsare the so-called aminated polyethers in which all or a portion of thehydroxyl groups of a polyether polyol are converted to primary orsecondary amine groups. Suitable such aminated polyethers are sold byHuntsman Chemicals under the trade name JEFFAMINE®. Typical conversionsof hydroxyl to amine groups for these commercial materials range fromabout 70-95%, and thus these commercial products contain some residualhydroxyl groups in addition to the amine groups. Preferred among theaminated polyethers are those having a weight per isocyanate-reactivegroup of about 100-1700, and having 2-4 isocyanate-reactive groups permolecule. These amine-containing materials advantageously constitute nogreater than about 5 weight percent, preferably from about 0.25 to about2 weight percent of the total weight of the isocyanate-reactivecomponent. When used in such small amounts, these components alsocontribute to a fast initial viscosity build, without unduly decreasingcream time.

In order to make the desired rigid foam, the isocyanate reactivematerials used in the isocyanate-reactive component preferably have anaverage nominal functionality of from about 2.2 to about 8, preferablyfrom about 2.5 to about 5.0, most preferably from about 2.5 to about 4.0isocyanate-reactive hydroxyl groups per molecule. In addition, theequivalent weight (weight per equivalent of isocyanate-reactive groups)of the fully formulated isocyanate-reactive component is advantageouslyfrom about 100 to about 300, preferably from about 150 to about 250.Accordingly, the functionality and equivalent weight of the individualpolyols are preferably selected so the foregoing parameters are met.

In addition, the selection of polyols influences the reactivity of theisocyanate-reactive component with the polyisocyanate. In general,primary hydroxyl groups are more reactive with a polyisocyanate than aresecondary hydroxyl groups. However, polyols that contain amine groupstend to be autocatalytic.

The isocyanate-reactive component also contains a blowing agent.Although physical blowing agents such as fluorocarbons,hydrofluoro-carbons, chlorocarbons, chlorofluorocarbons,hydrochlorofluorocarbons can be used, the preferred blowing agent iswater. Water reacts with the polyisocyanate to form carbon dioxide gasthat causes the reaction mixture to expand. The blowing agent is used inan amount sufficient to provide the foam with the aforementioneddensities. Preferably, enough blowing agent is used to expand thereactive components of the formulation (i.e., the non-syntactic phase,excluding the microspheres, fillers and other non-reactive materials) atleast about 100%, more preferably 150%, relative to the volume of theunfoamed reactive raw materials, as described before.

When water is used as the blowing agent, about 0.2 to about 2,preferably from about 0.4 to about 1.5 parts by weight are used per 100parts of other isocyanate-reactive materials in the isocyanate-reactivecomponent.

The isocyanate-reactive component additionally contains a thixotropicagent in an effective amount. The thixotropic agent is a material thatimparts shear-sensitive viscosity, i.e. the isocyanate-reactivecomponent containing the thixotropic agent exhibits a lower viscositywhen under shear than it exhibits under no or low shear conditions. Thischaracteristic permits the isocyanate-reactive component to be moreeasily blended with the polyisocyanate component despite the relativelyhigh viscosities of each. At the same time, this characteristic causesthe resulting reaction mixture to reassume a high viscosity once it isdispensed and no longer subject to shearing forces, thus controlling theamount of flow from the area and through holes or poorly sealed seams

Suitable thixotropic agents include fumed silica and certain clays suchas bentonite clay and montmorillonite clay. Fumed silica is a preferredthixotropic agent, and hydrophobic forms of fumed silica are mostpreferred. The thixotropic agent is used in an effective amount, forexample about 0.5 to about 5, preferably from about 1 to about 3 percentof the total weight of the isocyanate-reactive component

The aforementioned polyols, amine-terminated compounds and water tend tohave individual viscosities of about 20,000 cps or less, and often lessthan 5000 cps. Although the thixotropic agent tends to increase theviscosity, it is usually necessary to include a filler in order toachieve the necessary minimum viscosity described above. Accordingly, inorder to obtain the necessary minimum viscosity, the isocyanate-reactivecomponent will usually contain a filler or other material that increasesits viscosity. This is preferably accomplished by loading theisocyanate-reactive component with hollow microspheres, although otherfiller materials can be used alone or in conjunction with themicrospheres. When the preferred hollow microspheres are used, theygenerally constitute from about 5%, preferably from about 15%, morepreferably from about 20% to about 40%, preferably to about 35%, morepreferably to about 30% percent of the total weight of theisocyanate-reactive component. Other fillers can be used in similaramounts.

Suitable microspheres include those made from inorganic materials suchas glass and silica-alumina ceramics or polymeric materials such asepoxy resin, unsaturated polyester resin, silicone resin, phenolics,polyvinyl alcohol, polyvinyl chloride, polypropylene, and polystyrene.In addition, fly ash that is in the form of hollow particles can beused. Examples of commercially available fly ash of this type is sold byBoliden Intertrade, Inc., under the trade names Fillite 100 and Fillite150. Glass microspheres are most preferred. These microspheres mostadvantageously have average diameters of from about 5 to about 150microns, preferably from about 20 to about 85 microns. The microspheresadvantageously have a burst pressure sufficient to withstand the forcesimposed upon them during the formulation, mixing and dispensingprocesses. Microspheres having an 80% or greater survival rate whenexposed to at least 750 psi are preferred, and those having an 80% orgreater survival rate when exposed up to 5500 psi are more preferred. Inaddition, the microspheres advantageously have a bulk density of fromabout 0.1 to about 0.5 g/cc.

If desired, the microspheres may be surface treated with an interfacialadhesion promoter such as a silane compound.

In addition to providing increased viscosity and reducing the bulkdensity of the foam, the hollow microspheres may also act as nucleationsites for the generation of cells in the polyurethane foam matrix. Themicrospheres also serve as a reinforcing filler to provide increasedcompressive modulus.

Other fillers can be used in addition to, or less preferably in placeof, the microspheres. However, at least one of the isocyanate-reactiveand polyisocyanate components must contain the microspheres. Anon-exhaustive list of suitable alternative or supplemental fillersincludes talcs, clays, silicas, calcium carbonates, graphites, glass,carbon black, plastic powders such as ABS, and the like. Fibers such asglass or other ceramics, carbon, metals, or polymers such polyamide(i.e., Kevlar), propylene or the like are also useful fillers. Fiberspreferably have an aspect ratio of at least 5, preferably at least 20,and should be well-dispersed in the polyurethane matrix.

The isocyanate-reactive component may also contain auxiliary additivesthat promote the formation of a good quality, stable foam. Suchadditives include, for example, catalysts, surfactants, pigments,plasticizers, and the like. Suitable catalysts include the well knownpolyurethane catalysts such as are described at column 6 of U.S. Pat.No. 5,817,860, incorporated herein by reference. Preferred catalystsinclude salts and chelates of tin, zinc, bismuth, iron, mercury and thelike, as well as tertiary amine compounds. Organotin catalysts such asstannous octoate, stannous oleate, stannic chloride, dimethyltindilaurate and dibutyltin dilaurate are preferred metallic catalysts. Apreferred tertiary amine catalyst is triethylenediamine, which iscommercially available as a 33% by weight solution. Other suitabletertiary amine catalysts include trimethylamine, triethylamine,N-methylmorpholine, N,-ethylmorpholine, N,N-dimethylbenzylamine,N,N-dimethylethanolamine, N,N-dimethylpiperazine,1,4-diazobicyclo[2,2,2]octane, bis(dimethylaminoethyl)ether,bis(2-dimethylaminoethyl)ether, morpholine, N,N-dimorpholinediethylether, N,N-dimethylcyclohexylamine and4,4′-(oxydi-2,1-ethanediyl)bis.

Catalysts that can be stably dispersed in the polyisocyanate may insteador in addition be used in the polyisocyanate component.

The amount of catalyst is selected to provide a desired reaction rate.Generally, a relatively slow rate is desired, as this facilitates thedispensing of large shots of the mixture in large cavities, facilitateslonger static mixer life and/or it minimizes the amount of purgingnecessary to keep the mixer free of cured material. Sufficient catalystto provide a cream time (start of foam rise) of about 3-5 minutes, a geltime of about 6-12 minutes and tack free time of about 13-20 minutes ispreferable.

Suitable surfactants include the well-known silicone surfactants. Theseinclude commercially available polysiloxane/polyether copolymers such asTegostab (trademark of Goldschmidt Chemical Corp.) B-8462 and B-8404,and DC-198 and DC-5043 surfactants available from Dow Corning.

A preferred isocyanate-reactive component is formulated from a mixtureof components as follows:

125-250 equivalent weight, 2-8 functional polyester or polyether basepolyol, 15-85% by weight; 800-3000 equivalent weight 2-4 functionalpolyether polyol, 10-30% by weight; 125 or less equivalent weightcrosslinker, 2-15% by weight; amine-initiated polyether polyol, 0-5% byweight; amine-functional compound, 0-2% by weight; water, 0.2 to 1.5% byweight; microspheres, 15-40% by weight; thixotropic agent, 1 to 3% byweight; the isocyanate-reactive component may also contain auxiliarycomponents such as one or more catalysts and one or more surfactants.

A more preferred isocyanate-reactive component is formulated from amixture of components as follows: 125-250 equivalent weight, aromaticpolyester polyol, 15-40% by weight; 800-2000 equivalent weight 2-4functional polyether polyol containing dispersed polymer particles,15-30% by weight; 125 or less equivalent weight crosslinker, 4-10% byweight; amine-initiated polyether polyol, 1-4% by weight;amine-functional compound, 0.25-2% by weight; water, 0.4 to 1.2% byweight; microspheres, 15-30% by weight; thixotropic agent, 1 to 3% byweight; and effective amounts of one or more auxiliary components suchas one or more catalysts and one or more surfactants.

The polyisocyanate component comprises a polyisocyanate compound and athixotropic agent. Suitable polyisocyanates include those commonly usedin preparing polyurethanes, including aromatic, aliphatic andcycloaliphatic polyisocyanates. Aromatic polyisocyanates are generallypreferred based on cost, availability and properties. Exemplarypolyisocyanates include, for example, m-phenylene diisocyanate, 2,4-and/or 2,6-toluene diisocyanate (TDI), the various isomers ofdiphenymethanediisoyanate (MDI), hexamethylene 1,6-diisocyanate,tetramethylene-1,4-diisocyanate, cyclohexane-1,4-diisocyanate,hexahydrotoluene diisocyanate, hydrogenated MDI (H₁₂ MDI),naphthylene-1,5-diisocyanate, methoxyphenyl-2,4-diisocyanate,4,4′-biphenylene diisocyanate, 3,3′-dimethyoxy-4,4′-biphenyldiisocyanate, 3,3′-dimethyldiphenylmethane-4,4′-diisocyanate,4,4′,4″-triphenylmethane diisocyanate, polymethylenepolyphenylisocyanate, toluene-2,4,6-trilsocyanate, and4,4′-dimethyldiphenylmethane-2,2′,5,5′-tetraisocyanate. Preferredpolyisocyanates include TDI, MDI and the so-called polymeric MDIproducts, which are a mixture of polymethylene polyphenylisocyanates inmonomeric MDI. Especially suitable polymeric MDI products have a freeMDI content of from about 5 to about 40% by weight, more preferablyabout 10 to about 25% by weight, and have an average functionality(number of isocyanate groups per molecule) of about 2.8 to 4.0, morepreferably about 2.7 to about 3.4. Such polymeric MDI products areavailable from The Dow Chemical Company under the trade name PAPI®.

In addition to the foregoing polyisocyanates, prepolymers and quasi-(orsemi-) prepolymers thereof are useful and even preferred. Of particularinterest are prepolymers or quasi-prepolymers of polymeric MDI products,which prepolymers have an MDI content of less than about 20, preferablyless than about 10, especially less than about 6 weight percent. Theprepolymers or quasi-prepolymers of interest more suitably have anisocyanate equivalent weight of from about 175-500, especially about 200to about 350. These prepolymers are conveniently made by reacting anexcess of the polyisocyanate with a polyol. These prepolymers have a lowfree MDI content, so their use substantially reduces the risks of MDIinhalation exposure. Thus, by using the prepolymer approach to reducethe level of free MDI, costly engineering controls such as properdowndraft ventilation can be substantially reduced or potentiallyeliminated.

A polyisocyanate of particular interest is a quasi-prepolymer preparedin the reaction of an organic polyisocyanate, especially polymeric MDI,with a small quantity of a monoalcohol and a polyol that has an averagenominal functionality of about 1.8 to about 3.0. In making aquasi-prepolymer useful herein, the NCO:OH ratio ranges from about 2.5to about 5, preferably to about 4, and the equivalent ratio ofmonoalcohol to polyol is from about 1.75 to about 3.25, especially fromabout 2.25 to about 2.75. The quasi-prepolymer preferably has afunctionality of at least about 2.0 to about 3.0 and an NCO content ofabout 10-20% by weight. Among the quasi-prepolymers of this general typeare those described in U.S. Pat. No. 5,817,860, incorporated herein byreference.

The polyisocyanate component also includes an effective amount of athixotropic agent of the type discussed before. As before, fumed silicais a preferred thixotropic agent and hydrophobic types of fumed silicaare especially preferred. A suitable amount is from about 0.5 to about5, preferably from about 1 to about 3 percent of the total weight of thepolyisocyanate component.

As with the isocyanate-reactive component, it is usually necessary toincorporate a filler into the polyisocyanate component in order toattain the necessary viscosity. Suitable fillers for the polyisocyanatecomponent are the same as can be used in the isocyanate-reactivecomponent, with the hollow microspheres discussed above being highlypreferred. The amount of filler is selected so that the aforementionedviscosity is attained. For hollow microspheres, this is generallyaccomplished when the microspheres constitute about 5, preferably about10, more preferably about 12 weight percent, to about 35, preferablyabout 25, more preferably about 20 percent of the total weight of thepolyisocyanate component. Other fillers can substitute for all or aportion of the microspheres, as discussed with respect to theisocyanate-reactive component.

Note that at least one of the two reactive components, i.e., one of theisocyanate-reactive component and the polyisocyanate component, mustcontain hollow microspheres. However, the concentration of microspheresin each component need not be equal and can be significantly differentif necessary to desirably control component viscosity, the —NCO/OHstoichiometric mix ratio, volume ratios of the two components, and thelike.

In addition, the polyisocyanate component may contain various optionalingredients such as catalysts, colorant (i.e. pigments or dies),plasticizers, surfactants, blowing agents and the like. Suitableplasticizers include phthalate esters such as dioctyl phthalate,dimethyl phthalate, dibutyl phthalate, mixtures of such phthalate esterssuch as are sold by BASF Corporation under the trade name PALATINOL®;phosphate esters such as tributyl phosphate, triphenyl phosphate andcresyl diphenyl phosphate, chlorinated biphenyls, and aromatic oils. Theamount of plasticizer may range from about 1, preferably about 10, toabout 50, preferably about 25 percent of the weight of thepolyisocyanate component.

Preferably, at least one of the components will contain a pigment, andthe other has either no pigment or a pigment of a different color. Apreferred pigment is carbon black, which is used in only one of thecomponents. The use of a pigment in this manner provides a simple visualmethod for detecting incomplete mixing of the isocyanate-reactive andpolyisocyanate components, or off-ratio mixing. For example, if carbonblack is used in the polyisocyanate component, then proper mixing willresult in a uniformly gray mixture. A mixture that is too white impliesthat the mixture is polyol rich. A mixture that is too black impliesthat the mixture is too rich in polyisocyanate. A mixture that hasstreaks would imply poor mixing.

Foam according to the invention is prepared by mixing theisocyanate-reactive and polyisocyanate components and applying thethus-formed reaction mixture to/into the part/cavity to be reinforced.Because of the high viscosity of the isocyanate-reactive andpolyisocyanate components, mixing is conveniently done by forcing themthrough a static mixer. The length, diameter, materials of construction,the number and design of the elements contained in these static mixersvary depending upon vendor design, but they all generally work on theprinciples of dividing and recombining materials flowing through them.Because both the isocyanate-reactive and polyisocyanate components arethixotropic, the shear introduced by the dispensing equipment and thestatic mixer operates to somewhat reduce the viscosity of thecomponents, thus facilitating better, easier mixing.

The ratios of the two components are advantageously selected so as toprovide an isocyanate index (ratio of NCO to isocyanate-reactive groups)of about 0.7, preferably about 0.9, more preferably about 0.98, to about1.5, preferably to about 1.25, more preferably to about 1.1. It isespecially preferred to formulate the isocyanate-reactive andpolyisocyanate components so that these isocyanate indices are achievedusing comparable volumes of each component. Preferably, theisocyanate-reactive component and the isocyanate component are mixed ina volume ratio of from about 4:1 to 1:4, preferably about 3:1 to 1:3,more preferably from about 2:1 to 1:2, most preferably about 1:1 toabout 1:2. This facilitates the dispensing of the components in anindustrial setting, and allows for the use of simpler mixing anddispensing equipment. For example, the isocyanate-reactive component andthe polyisocyanate component are conveniently packaged in commerciallyavailable cartridges. These cartridges are used in conjunction with adispensing gun that is adapted to dispense both components from theirrespective cartridges, through a static mixer, and onto/into the areabeing reinforced. Having the volumes of the two components being equalor in simple multiples of each other facilitates packaging thecomponents in cartridges in this manner.

The temperature of mixing and foaming is conveniently from about 50 toabout 100° F., although somewhat higher temperatures can be tolerated.

In order for efficient foaming to take place, nucleating sites areadvantageously provided. This is most conveniently done by dispersing aquantity of air, nitrogen, carbon dioxide or other inert gas into one orboth of the isocyanate-reactive and polyisocyanate components. Dispersedgasses provide effective nucleation when they constitute at least about2 volume percent (at STP) of the reaction mixture, preferably, at leastabout 4 volume percent of the reaction mixture. Generally, no more thanabout 15 volume percent of dispersed gasses are used and preferably, nomore than about 12 volume percent of dispersed gasses are used.

Nucleating gasses can be dispersed into the reaction mixture as theisocyanate-reactive and polyisocyanate components are mixed anddispensed. However, it is preferred to disperse the gas into one andpreferably both components prior to mixing. It is highly preferred todisperse similar volumes of gas into each component. This avoids mixingproblems associated with mixing components having significantlydifferent contents of dispersed gasses. Preferably, the percentage ofdispersed air content should not differ between the two components bymore than 8 percentage points. More preferably, the percentage ofdispersed air content in the two components should not differ by morethan 5 percentage points.

Because of the high viscosity of each of the isocyanate-reactive andpolyisocyanate components, gas can be dispersed into either or both,preferably both, of the components as each are manufactured. Thedispersed gas forms microscopic air bubbles that, due to the highviscosity of the components, tend to be stable (i.e. they do notsubstantially coalesce to form fewer, larger air bubbles) over a periodof months or more.

Once the reaction mixture is formed, it is dispensed and allowed toreact to form a foam. When a specific structural member is to bereinforced, the reaction mixture is conveniently dispensed on or intothe member at the point where reinforcement is desired. Alternately, thefoam can be formed separately and then glued or otherwise attached tothe structural member. It is usually not necessary to apply heat toeffect a full expansion and cure.

The syntactic/non-syntactic foam of the invention can be used in avariety of applications to structurally stiffen or reinforce areas towhich it is applied. Load beams, pillars, rocker panels, roof rails andheaders, cross members, and the like are examples of automotive bodystructural components that benefit from reinforcement from the foam ofthis invention. Many of these components are hollow. In some instances,the entire cavity will be filled by the foam. In other instances, thecavity may be only partially filled to provide increased stiffness orreinforcement in some localized area. In other instances, the foam ofthe invention may be applied to an area where two structural membersmeet, such as where vertical structural members meet horizontalstructural members.

The following examples are provided to illustrate the invention, but arenot intended to limit the scope thereof. All parts and percentages areby weight unless otherwise indicated.

EXAMPLES 1-3

A. Formulation of Isocvanate-reactive Component

Isocyanate-reactive components A, B and C are prepared from theingredients indicated in Table 1:

TABLE 1 Ingredient A (pbw) B (pbw) C (pbw) Polyester Polyol¹ 37.62 31.8533.22 Polymer Polyol A² 18.5 25.0 0 Polymer Polyol B³ 0 0 18.5 33%triethylene diamine solution⁴ 0.03 0 0.03 Polyether Polyol A⁵ 0 0 5.0Glycerol 7.8 7.0 7.0 Amine-initiated polyol⁶ 2.0 4.0 2.0 GlassMicrospheres⁷ 26.0 24.0 26.0 Surfactant A⁸ 3.0 0 3.0 Surfactant B⁹ 0 3.00 Water 0.80 0.9 0.85 Aminated Polyether¹⁰ 1.75 1.75 1.75 Fumed Silica¹¹2.5 2.5 2.5 ¹Stepanpol 3152, a 356 MW aromatic polyester diol sold byStepan Company; ²A 4300MW EO-capped poly(propylene oxide) nominal triolcontaining 40% dispersed styrene-acrylonitrile particles; ³Specflex ™NC-700 polyether polyol, sold by The Dow Chemical Company; ⁴Dabco 33LV;33% triethylenediamine, 67% dipropylene glycol, sold by Air Products;⁵Voranol ™ 490 polyol, a 490 MW rigid foam polyol sold by Dow Chemical;# ⁶Voranol ™ 800, a 280 MW amine-initiated tetrol sold by Dow Chemical;⁷VS500 glass microspheres, sold by 3M Company; ⁸Tegostab B-8404, sold byGoldschmidt Chemical Corporation; ⁹Tegostab B-8462, sold by GoldschmidtChemical Corporation; ¹⁰Jeffamine ™ T-403, a 440 MW nominallytrifunctional aminated polyether; ¹¹Cab-O-Sil TS-720, Cabot Corporation.

Isocyanate-reactive compositions A, B and C are prepared by mixing allcomponents except water and fumed silica in a Ross mixing vessel for 15minutes at 60 rpm. The water and fumed silica are then added and mixedfor additional 15 minutes at 60 rpm and a partial vacuum of 10 inches ofmercury. The water content of the composition is then measured andadjusted as necessary to the water contents indicated in Table 1. Themixture is then mixed an additional 15 minutes at 60 rpm and a partialvacuum of 10 inches of mercury. Isocyanate-reactive component A has aBrookfield viscosity of 151,000 cps at 25° C., number 7 spindle, 10 rpmand contains 9.4 volume % air. Isocyanate-reactive component B has aBrookfield viscosity, same conditions, of 208,000 cps and contains 7.5volume % air. Isocyanate-reactive component C has a Brookfieldviscosity, same conditions, of 200,000 cps and contains 11.9 volume %air.

B. Polyisocyanate Component Preparation

Polyisocyanate component A is made by mixing 7.8 parts of a 430 MWpolyoxypropylene diol (Voranol™ 220-260, available from the Dow ChemicalCompany), 6.95 parts of n-butanol, 65.23 parts of a polymeric MDI havinga free MDI content of about 20% and an isocyanate functionality of about3.2 (PAPI™ 20, from The Dow Chemical Company), 20 parts of Palatinol711P phthalic ester mixture and 0.013 parts of an organotin catalyst(Dabco T-9, from Air Products) in a Ross mixing vessel for 30 minutes at25° C. at 60 rpm under a nitrogen pad, followed by mixing for anadditional 60 minutes at 70° C. and 60 rpm. 83.98 parts of the resultingprepolymer are mixed with 0.025 parts carbon black (Monarch 120, fromCabot Corporation) and 14.0 parts VS5500 glass microspheres in a Rossmixing vessel at 70° C. and 60 rpm, with cooling to 35° C. When thetemperature reaches 35° C., 2 parts of Cab-O-Sil TS-720 fumed silica areadded, and the resulting mixture is stirred at 60 rpm for an additional15 minutes under a vacuum of 10 inches of mercury. Polyisocyanatecomponent A has a Brookfield viscosity of 250,000 cps (spindle 7, 25°C., 10 rpm). It contains 5.6 volume % air.

Polyisocyanate component B is made in a similar manner. The ingredientsused to make the prepolymer are 7.56 parts of Voranol 220-260 polyol,6.74 parts n-butanol, 63.19 parts of PAPI 20 polymeric MDI, 22.5 partsof the Palatinol 711P phthalic ester mixture and 0.013 parts of the T-9catalyst. 82.97 parts of the prepolymer are blended with 0.03 parts ofMonarch 120 carbon black, 15 parts of VS5500 glass microspheres and 2parts of Cab-O-Sil fumed silica in the same manner. Polyisocyanate B hasa Brookfield viscosity, under the conditions specified above, of 216,000cps and contains 4.6 volume % air.

C. Foam Preparation

Polyurethane foam Example 1 is prepared by mixing PolyisocyanateComponent A and isocyanate-reactive component A at a 2:1 volume ratio atroom temperature, and allowing 285 grams of the mixture to cure for 24hours in a 16 ounce cup. Example 1 has a free rise density of 22.9poundsper cubic foot. A 2″×2″×1″ skinless sample of the foam is tested formodulus on an Instron machine at a deflection rate of 0.1 inch/minute.The compressive modulus is 16,800 psi.

Polyurethane foam Example 2 is prepared by mixing PolyisocyanateComponent B and Isocyanate-reactive component B at a 2:1 volume ratio inthe same manner as Example 1 is prepared. Example 2 also has a free risedensity of 23.7 pounds per cubic foot. The compressive modulus at adeflection rate of 0.1 inch/minute is 10,844 psi.

Polyurethane foam Example 3 is prepared by mixing PolyisocyanateComponent A and Isocyanate-reactive Component C at a 2:1 volume ratio inthe manner just described. Example 3 has a free rise density of 23.3pounds per cubic foot. The compressive modulus at a deflection rate of0.1 inch/minute is 18,233 psi.

EXAMPLE 4

Isocyanate-reactive Component D is made in the same general manner asare Isocyanate-reactive Components A, B and C, using the componentslisted in Table 2. It has a Brookfield viscosity, under the conditionsdescribed above, of 89,600 cps. It contains 5.2 volume % air.

TABLE 2 Ingredient pbw Polyester Polyol¹ 19.85 Polymer Polyol A² 27.5Polyether polyol A³ 22.5 Glycerol 3 Amine-initiated polyol⁴ 2.0 GlassMicrospheres⁵ 22.0 Surfactant B⁶ 1.0 Water 0.4 Aminated Polyether⁷ 1.0Fumed Silica⁸ 0.75 ¹Stepanpol 3152, a 356 MW polyester diol sold byStepan Company; ²A 4300MW EO-capped poly(propylene oxide) nominal triolcontaining 40% dispersed styrene-acrylonitrile particles; ³Voranol ™ 490polyol, a 490 MW rigid foam polyol sold by Dow Chemical Company;⁴Voranol 800, a 280 MW amine-initiated tetrol sold by Dow Chemical;⁵VS500 glass microspheres, sold by 3M Company; ⁶Tegostab B-8462, sold byGoldschmidt Chemical Corporation; # ⁷Jeffamine ™ T-403, a 440 MWnominally trifunctional aminated polyether, ⁸Cab-O-Sil TS-720, CabotCorporation.

Polyisocyanate component C is prepared by mixing 74.9 parts of PAPI™ 20polymeric MDI, 0.1 part of Monarch 120 carbon black, 24 parts of VS5500glass microspheres and 1 part of Cab-O-Sil TS-720 fumed silica.Polyisocyanate Component C has a Brookfield viscosity, under theconditions described above, of 129,000 cps and contains 3.8 volume %air.

Polyurethane foam Example 4 is made from Polyisocyanate Component C andIsocyanate-reactive Component D in the same manner as Examples 1-3,except the volume ratio is 1:1 (isocyanate index 1.12). The foam has afree rise density of 19 pcf and a compressive modulus of 19,319 psi.

What is claimed is:
 1. A process for making a polyurethane foam,comprising (1) mixing under reaction conditions a high viscosityisocyanate-reactive component (a) and a high viscosity polyisocyanatecomponent (b), wherein component (a) includes at least one polyol, ablowing agent and at least one thixotropic agent, component (b) includesat least one polyisocyanate compound and at least one thixotropic agent,wherein one or both of components (a) and (b) contain a plurality ofhollow microspheres, and wherein each of said component (a) andcomponent (b) has a Brookfield viscosity (spindle 7, 25° C., 10 rpm) ofat least about 50,000 cps (50 Pa.s), and (2) allowing the mixture toexpand in place and cure.
 2. The process of claim 1, wherein the blowingagent comprises water.
 3. The process of claim 2, wherein component (a)contains from about 15 to about 30% by weight hollow microspheres andcomponent (b) contains from about 12 to about 25% by weight hollowmicrospheres.
 4. The process of claim 3, wherein the thixotropic agentis fumed silica.
 5. The process of claim 4, wherein component (a)contains from about 15-40% by weight of an aromatic polyester polyolhaving an equivalent weight of about 125-225.
 6. The process of claim 5,wherein component (a) further contains from about 4 to about 10% byweight of a crosslinker having an equivalent weight of below
 125. 7. Theprocess of claim 6, wherein component (a) further contains from about 1to about 4% by weight of an amine-initiated polyol.
 8. The process ofclaim 7, wherein component (a) further contains from about 0.25 to about2% of an amine-functional compound.
 9. The process of claim 8, whereincomponent (a) further contains from about 10 to about 30% by weight of a800-3000 equivalent weight, nominally 2-4 functional polyether polyol.10. The process of claim 3, wherein component (b) comprises a prepolymerof polymeric MDI, said prepolymer having a free MDI content of less thanabout 6% by weight and an isocyanate equivalent weight of about 200 toabout
 350. 11. The process of claim 2 wherein in step (2), the mixtureis dispensed on to or into a structural member and allowed to expand inplace and cure.
 12. The process of claim 11 wherein the structuralmember is an automotive body structural component.
 13. The process ofclaim 12 wherein the automotive body structural member includes a hollowcavity, and the mixture is dispensed into the cavity where it is allowedto expand in place and cure.
 14. The process of claim 12 wherein theautomotive body structural member is a load beam, pillar, rocker panel,roof rail, header or cross member.
 15. The process of claim 2 whereinthe isocyanate-reactive component and the polyisocyanate component aremixed by forcing them through a static mixer.
 16. The process of claim15 wherein in step (2), the mixture is dispensed on to or into astructural member and allowed to expand in place and cure.